1. Field of the Invention
This invention relates to circuit breakers for protecting electric power circuits and, more particularly, to such circuit breakers including a mechanism for breaking a tack weld between separable contacts.
2. Background Information
Circuit breakers used in residential and light commercial applications are commonly referred to as miniature circuit breakers because of their limited size. Such circuit breakers typically have a set of separable contacts opened and closed by a spring powered operating mechanism. A thermal-magnetic trip device actuates the operating mechanism to open the separable contacts in response to persistent overcurrent conditions and to short circuit conditions.
When a movable contact arm of a circuit breaker, electrical contactor or electrical relay is actuated, for example, by a solenoid or motor, it is necessary, under certain circumstances, to be able to open a relatively small tack weld that has formed on the faces of the separable contacts. In some circumstances, the actuating mechanism is not able to generate enough force on the movable contact arm to break the tack weld and open the separable contacts.
There is room for improvement in circuit breakers including a mechanism for breaking a tack weld between separable contacts.
These needs and others are met by the present invention, which provides improvements in rocking separable contacts, in order to achieve a peeling action on the separable contact faces, in combination with increasing the force of an actuator, such as a solenoid, in order to assist in breaking a relatively light tack weld.
Whenever an actuator, such as a solenoid, opens the separable contacts, the plunger of the solenoid freely moves a pivot of a movable contact arm to one end of a pivot opening. This accomplishes two purposes: (1) a peeling action is provided on the faces of the separable contacts, thereby reducing the force needed to break the tack weld; and (2) a gap within the solenoid between the solenoid core and the solenoid plunger is reduced, thereby increasing the opening force of the solenoid plunger. These synergistic actions reduce the force needed to break the tack weld and, also, increase the opening force as provided by the solenoid plunger, in order to break such tack weld.
In accordance with the invention, an electrical switching apparatus comprises: a housing comprising a pivot opening having a first end and a second end; a movable arm including a first portion having a pivot pivotally mounted in the pivot opening and a second portion, the pivot opening being substantially larger than the pivot; a fixed contact mounted in the housing; a movable contact mounted on the second portion of the movable arm, the fixed contact, the movable contact and the movable arm cooperating.to provide a closed state, a pivot state and an open state; an actuator mounted in the housing, the actuator including a member coupled to the movable arm, the actuator moving the member between a first position and a second position to provide the open state and the closed state, respectively, the member having a third position between the first position and the second position; and means for biasing the movable arm toward the fixed contact to maintain the closed state; wherein the closed state is defined by the second position of the member of the actuator, with the pivot engaging the second end of the pivot opening and being apart from the first end of the pivot opening, wherein the pivot engages the first end of the pivot opening and is apart from the second end of the pivot opening in the pivot state, wherein the open state is defined by the first position of the member of the actuator, with the pivot engaging the first end of the pivot opening and being apart from the second end of the pivot opening, and wherein when the fixed contact and the movable contact are welded closed, the actuator provides insufficient force to move the member of the actuator to the first position until after the pivot moves apart from the second end of the pivot opening and at least substantially toward the first end of the pivot opening.
The actuator may be a solenoid having a core and at least one coil wound on the core, and the member may be a plunger of the solenoid. The plunger may engage the core in the first position, be set apart from the core with a first gap in the third position, and be further set apart from the core with a larger second gap in the second position. The at least one coil may include a closing coil and an opening coil, and the opening coil may energize the core to attract the plunger with a first force in the third position, and a second smaller force in the second position.
The pivot may have a size within the pivot opening. A distance between the first end and the second end of the pivot opening may be about twice the size of the pivot.
As another aspect of the invention, a remotely controllable circuit breaker comprises: a housing comprising a pivot opening having a first end and a second end; a first terminal; a second terminal; a set of first contacts mounted in the housing; an operating mechanism mounted in the housing and coupled to the set of first contacts for opening and closing the set of first contacts; a movable arm including a first portion having a pivot pivotally mounted in the pivot opening and a second portion, the pivot opening being substantially larger than the pivot; a set of second contacts comprising a fixed contact mounted in the housing and a movable contact mounted on the second portion of the movable arm, the fixed contact, the movable contact and the movable arm cooperating to provide a closed state, a pivot state and an open state, the set of second contacts being electrically interconnected with the set of first contacts between the first and second terminals; a remotely controllable solenoid including a member coupled to the movable arm, the remotely controllable solenoid moving the member between a first position and a second position to provide the open state and the closed state, respectively, the member having a third position between the first position and the second position; and means for biasing the movable arm toward the fixed contact to maintain the closed state, wherein the closed state is defined by the second position of the member of the actuator, with the pivot engaging the second end of the pivot opening and being apart from the first end of the pivot opening, wherein the pivot engages the first end of the pivot opening and is apart from the second end of the pivot opening in the pivot state, wherein the open state is defined by the first position of the member of the actuator, with the pivot engaging the first end of the pivot opening and being apart from the second end of the pivot opening, and wherein when the fixed contact and the movable contact are welded closed, the actuator provides insufficient force to move the member of the actuator to the first position until after the pivot moves apart from the second end of the pivot opening and at least substantially toward the first end of the pivot opening.
The fixed contact and the movable contact may include opposing faces, which are engaged in the closed state and are disengaged in the open state. When the opposing faces are welded closed, the pivot state separates a portion of the opposing face of the movable contact from the opposing face of the fixed contact.
As another aspect of the invention, an electrical switching apparatus comprises: a housing; a movable arm including a first portion and a second portion; means for mounting the first portion of the movable arm for pivotal movement and longitudinal movement with respect to the housing; a fixed contact mounted in the housing; a movable contact mounted on the second portion of the movable arm, the fixed contact, the movable contact and the movable arm cooperating to provide a closed state, a pivot state and an open state; and an actuator mounted in the housing, the actuator including a member coupled to the movable arm, the actuator moving the member between a deactuating position and an actuating position to provide the open state and the closed state, respectively, the member having a pivot position between the deactuating position and the actuating position, wherein the closed state is defined by the actuating position of the member of the actuator, wherein the first portion of the movable arm moves to a first longitudinal position in the pivot state and in the open state, wherein the first portion of the movable arm moves to a second longitudinal position in the closed state, and wherein when the fixed contact and the movable contact are welded closed, the actuator provides insufficient force to move the member of the actuator to the deactuating position until after the first portion of the movable arm moves at least substantially toward the first longitudinal position in the pivot state.